I'm in a location where pretty much everyone in the local beekeeping association is using Nationals with deep 14x12 brood boxes.

Personally, I'm torn between a hTBH and buying Rose OSB; with a small thought about just buying a National hive to be compatible while I learn.

The current thought process I'm going through is "what to do with the nuc"?

The bees I get will probably be on a nuc. There is a small chance I'll get a swarm from one of the local association members, but this is unlikely. I'll either get a split from an association hive or a farmed nuc and these will be in a 14x12 compatible frames.

I currently have two 5 frames nucs in dadant hives that I plan to move into htbh.

What I do usually (yes, I did it many years, for warré and hktbh) is :
- during a sunny day when most foragers are out
- smoke the hive and wait a bit, let the bee take as much honey as possible
- shake all frames into a larger box, check the source hive is empty
- put back the frames (check again the queen is not there)
- you can then drop your bees into a new hive, I often keep them 1-3 days in the cellar, this is recommended if the old and new hive will be in the same location
- feed a lot if you don't have built combs

After 30 days the original hive will have a new queen, check the brood (there will be only larvaes), you can shake again. For the records, I did it last year but late in the season, so I decided to not shake a second time and winter the bees for this year.

This method looks a bit brutal, but in my experience the bees keep calm if you do it quickly.

This is one "easy" solution that only require a larger box and that can be used to create an artificial swarm but I've looked at the link you provided and it looks very interesting, although technically more complex.

I'll move 6 full Dadant frames tomorrow. If I spot the queen I'll try to catch her and let her in the top bar part with the queen excluder.
If not, I'll simply check the next days, I've added some built bars and hope the queen will quickly move there to lay eggs.

I'm just afraid that the bees will eventually move to the top bar area and use the dadant area to store honey as soon as the top bar area is filled (the hive is not hyper large, only 24 bars). I'll have to check it often and remove some bars to start new nucs to avoid swarming.

Conserving wild bees

Research suggests that bumble bee boxes have a very low success rate in actually attracting bees into them. We find that if you create an environment where first of all you can attract mice inside, such as a pile of stones, a drystone wall, paving slabs with intentionally made cavities underneath, this will increase the success rate.

Most bumble bee species need a dry space about the size a football, with a narrow entrance tunnel approximately 2cm in diameter and 20 cm long. Most species nest underground along the base of a linear feature such as a hedge or wall. Sites need to be sheltered and out of direct sunlight.